Choosing a cam for my engine?
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From: Morton Grove Illinois
Alright, tomorrow once I get back from school I'll be pulling the intake off again to reseal it and make sure I don't get any vacuum leaks. I saw that when I had some spilled oil on the intake that right in the middle I have an exhaust leak through the exhaust crossover (no EGR on this manifold) and it was blowing bubbles. That's where I thought that since that was leaking, there's a pretty large chance the intake is leaking too.
Burning Brakes
Joined: Nov 2012
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From: Indianapolis IN
Do you have anyone that would loan you a stock spreadbore intake to test with, because I doubt your carb adapter is causing the problem you're describing.
The carb to manifold mismatch is at the secondary bores with your adapter.
That is a great carb, I'd prefer it over a square bore holley.
I've used a Comp 262HE in a low compression 350 and it had plenty of low-end punch. I've got your current cam (262XE) on the shelf that was destined for a different low-comp 350 build.
The carb to manifold mismatch is at the secondary bores with your adapter.
That is a great carb, I'd prefer it over a square bore holley.
I've used a Comp 262HE in a low compression 350 and it had plenty of low-end punch. I've got your current cam (262XE) on the shelf that was destined for a different low-comp 350 build.
Race Director
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From: Millington Illinois
St. Jude Donor '08-'09
Alright, tomorrow once I get back from school I'll be pulling the intake off again to reseal it and make sure I don't get any vacuum leaks. I saw that when I had some spilled oil on the intake that right in the middle I have an exhaust leak through the exhaust crossover (no EGR on this manifold) and it was blowing bubbles. That's where I thought that since that was leaking, there's a pretty large chance the intake is leaking too.
Burning Brakes
Joined: Nov 2012
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From: Indianapolis IN
This would create a mismatch with a new intake.
Follow 63Mako's test.
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From: Morton Grove Illinois
Before you pull the intake. Disconnect and plug all the vacuum lines at the carb and intake except the vac advance can. Pull the line off the carb going to the vacuum advance can and suck on it. It should pull the advance plate and then you can't suck any air through it. That eliminates any leaks outside the intake/adapter/carb. Then check vacuum with your guage. If it jumps up to about steady 17.5 at 800 no load RPM the leak is not at the intake. If it don't increase spray a little carb cleaner around the base of the carb adapter and carb base. If it is leaking at the base you will rev a little when it sucks in the carb cleaner. If that all checks out you have a manifold leak.
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From: Morton Grove Illinois
Alright, I'll see if there's any obvious leaks and if I can't find anything I'll throw the performer back on and see
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
You can buy the Performer RPM with a spreadbore flange (7104), in case you were not aware of that. Maybe you can clean it up thoroughly and return it? I don't think the adapter is the cause of your problem, but I still don't like them, especially the ones that adapt a spreadbore carb to a square flange. Anyway, looks like you have some good advice to work with here, and since you're planning to upgrade heads, you should have a rockin' little powerplant there when you are finished, good luck!
Scott
Scott
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From: Morton Grove Illinois
I fired her up today to find any possible vacuum leaks and I couldn't find any. What I did find however when I checked the temp on each header was that my #5 cylinder was wwaayyy colder then the rest and I found an arcing spark plug wire, so I'll be getting new wires. It didn't solve the vacuum problem but it did go out, it sits at 15 inches now. And I do have a good amount of power down low now but it still takes off stronger above 4000, so any tips on tuning the carb? I think that could possibly be it. I have it tuned a little richer then I had it before the cam swap, but I'm not expert on carbs.
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From: Morton Grove Illinois
You can buy the Performer RPM with a spreadbore flange (7104), in case you were not aware of that. Maybe you can clean it up thoroughly and return it? I don't think the adapter is the cause of your problem, but I still don't like them, especially the ones that adapt a spreadbore carb to a square flange. Anyway, looks like you have some good advice to work with here, and since you're planning to upgrade heads, you should have a rockin' little powerplant there when you are finished, good luck!
Scott
Scott
Last edited by Conrad Celinski; Jan 16, 2014 at 04:03 PM.
Burning Brakes
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From: Indianapolis IN
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From: Morton Grove Illinois
I did not degree the cam, and I set it in with both timing dots matched together to make sure I get the valve timing right. And I made sure that I set the crank gear in the standard valve timing slot and not 4* advanced or 4* retarded. I just found a vacuum leak right behind the carb at the fitting that goes to the brake booster, and that brought my vacuum up to 16 inches
Burning Brakes
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From: Indianapolis IN
There ya go, now the power should come on much faster.
I hope the valve timing is ok, but with quality control the way it is nowdays it is really best to degree the cam to be sure.
I've not used any of the Comp XE cams in my engines yet,( my buddy's 396 - yes ), but the 262HE (212 @ .050) had more power below 4,000 than the 268HE (218 @ .050) in Comp's dyno curve.
yours should be at least between the two of those in my opinion. Probably closer to the old 268HE .
The Performer will probably give you a better feel of more bottom-end torque, but the RPM would probably run faster in the quarter mile. (hope that makes sense)
I hope the valve timing is ok, but with quality control the way it is nowdays it is really best to degree the cam to be sure.
I've not used any of the Comp XE cams in my engines yet,( my buddy's 396 - yes ), but the 262HE (212 @ .050) had more power below 4,000 than the 268HE (218 @ .050) in Comp's dyno curve.
yours should be at least between the two of those in my opinion. Probably closer to the old 268HE .
The Performer will probably give you a better feel of more bottom-end torque, but the RPM would probably run faster in the quarter mile. (hope that makes sense)
Safety Car
Joined: Jan 2009
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From: anchorage ak
I fired her up today to find any possible vacuum leaks and I couldn't find any. What I did find however when I checked the temp on each header was that my #5 cylinder was wwaayyy colder then the rest and I found an arcing spark plug wire, so I'll be getting new wires. It didn't solve the vacuum problem but it did go out, it sits at 15 inches now. And I do have a good amount of power down low now but it still takes off stronger above 4000, so any tips on tuning the carb? I think that could possibly be it. I have it tuned a little richer then I had it before the cam swap, but I'm not expert on carbs.
Last edited by bluedawg; Jan 16, 2014 at 09:23 PM. Reason: shittty spelling and dropped beer.
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From: Millington Illinois
St. Jude Donor '08-'09
I did not degree the cam, and I set it in with both timing dots matched together to make sure I get the valve timing right. And I made sure that I set the crank gear in the standard valve timing slot and not 4* advanced or 4* retarded. I just found a vacuum leak right behind the carb at the fitting that goes to the brake booster, and that brought my vacuum up to 16 inches
Race Director
Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
http://www.lbfun.com/warehouse/tech_...t%20Timing.pdf
http://www.lbfun.com/warehouse/tech_...ance_Specs.pdf
These two papers will help you out. Need a vacuum advance can that matches your new vacuum readings and a timing curve that is 36 degrees with vacuum advance disconnected and plugged all in @ 2800 or so. Then hook your correct vacuum can back up and let us know how it does. Don't mess with the carb until it is firing on all cylinders and the timing and curve are set up right. Then, and only then go through the carb. Here is a great link for that.
http://www.lbfun.com/warehouse/tech_...rb%20Paper.pdf
If you have good compression, no vacuum leaks and good spark to all cylinders and follow these papers you will have a great performing engine for not much cash investment, just time investment and you will learn a lot about performance tuning a carberated engine which is a lost art. Run the Performer intake as it matches your cam well. Cam operating range is 1300 to 5600. Performer operating range is idle to 5500.
http://www.lbfun.com/warehouse/tech_...ance_Specs.pdf
These two papers will help you out. Need a vacuum advance can that matches your new vacuum readings and a timing curve that is 36 degrees with vacuum advance disconnected and plugged all in @ 2800 or so. Then hook your correct vacuum can back up and let us know how it does. Don't mess with the carb until it is firing on all cylinders and the timing and curve are set up right. Then, and only then go through the carb. Here is a great link for that.
http://www.lbfun.com/warehouse/tech_...rb%20Paper.pdf
If you have good compression, no vacuum leaks and good spark to all cylinders and follow these papers you will have a great performing engine for not much cash investment, just time investment and you will learn a lot about performance tuning a carberated engine which is a lost art. Run the Performer intake as it matches your cam well. Cam operating range is 1300 to 5600. Performer operating range is idle to 5500.
Last edited by 63mako; Jan 16, 2014 at 10:06 PM.
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From: Morton Grove Illinois
Thanks for the links! Those will really help. It didn't even come to me that with reduced vacuum compared to stock the vacuum advance won't work as intended. I haven't driven it since I fixed the vacuum leak and tweaked the carb a bit so I can't say how its running, it started snowing again today 
. I haven't changed jet sizes yet because I'm still deciding if I'm going to change carbs in the spring to match the intake (plus shorten the height a bit). And yes, I did recurve the distributor, one of the first things I did because when I bought the car the vacuum advance didn't worked and had a massive leak (was basically a straw) and the mechanical advance in the distributor was siezed up and didn't move at all. I bought a recurve kit and used the weakest springs so the total advance at 2500rpm was 36 degrees. And so I should for sure run the performer instead of the RPM? I'll sacrifice just a bit of bottom end for an increased 1/4 mile with this cam, plus I feel that the rpm will help me with new heads this summer
. I haven't changed jet sizes yet because I'm still deciding if I'm going to change carbs in the spring to match the intake (plus shorten the height a bit). And yes, I did recurve the distributor, one of the first things I did because when I bought the car the vacuum advance didn't worked and had a massive leak (was basically a straw) and the mechanical advance in the distributor was siezed up and didn't move at all. I bought a recurve kit and used the weakest springs so the total advance at 2500rpm was 36 degrees. And so I should for sure run the performer instead of the RPM? I'll sacrifice just a bit of bottom end for an increased 1/4 mile with this cam, plus I feel that the rpm will help me with new heads this summer
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From: Morton Grove Illinois
Update: I love the new cam. I got the vacuum issues sorted out which all came from around the carb and then one from the headlight switch (left it connected but disconnected/plugged the line up by the actuators). The thing pulls a lot harder now once it hits 2000 rpm. I know it should lower, I just don't have the carb tuned anywhere near perfect (jets and accelerator arm). Its 10 degrees out now so no rush. Its a lot closer to what I'm looking for out of it, hopefully the heads will bring it right up to where I want it.
What do I need in order to bring the stock 8.5:1 compression up to around 10:1 ratio? THin head gaskets? If I get everything planned out, I'll possibly do this all within a month or two. What do the intake runner sizes mean on heads? I'm assuming that higher revving, bigger engines need bigger size ports.
(Should I be starting a new thread?... This started as just choosing a cam, and I'm ending up replacing everything but my bottom end)
What do I need in order to bring the stock 8.5:1 compression up to around 10:1 ratio? THin head gaskets? If I get everything planned out, I'll possibly do this all within a month or two. What do the intake runner sizes mean on heads? I'm assuming that higher revving, bigger engines need bigger size ports.
(Should I be starting a new thread?... This started as just choosing a cam, and I'm ending up replacing everything but my bottom end)
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
If your compression ratio is actually 8.5:1 right now, then a Felpro 1094 head gasket, .015" compressed thickness, along with some 64cc combustion chamber heads, should get you somewhere around 9.5:1. Your present compression ratio is probably more like 8:1 now, so you're probably looking at about 9:1 with the new heads and gasket. If you could find some heads with 58cc chambers, you'd be looking at closer to 9.5:1. If you want to go higher than that, you're looking at milling heads, or buying new flat-top pistons.
Scott
Scott
